Pressure tube for traffic indicator



R. L. ROBY 3, UBE FOR IC INDICATOR F'i llllllllllll 61 INVENTOR. ROBERT L. ROBY Y United States atcnt 3,090,404 Patented May 21, 1963 Free This invention relates to pressure tubes, and more particularly to tubes of this type that are used to activate devices that count traflic, switch signals, open or close doors, or perform some similar work.

BACKGROUND As is well known, traflic signals are frequently arranged to favor a busy street; but a device in the side street trips the signal when a vehicle passes over the device. These trippers are frequently buried in the roadway, and are thus subject to drippage of rain water, dirt, and the like.

Another use of these trippers is to count vehicles passing a given spot. This information aids traflic authorities in planning roads and highways, establishing patterns for turns and signal lights, determining the type of pavement and repairs that would be most satisfactory, and helps them in many other ways.

It is also desirable to alert the operator of service stations when a car drives in. Another, but similar situation, requires that a door be opened or closed when a person or vehicle passes a given location. Other situations of this general type will be familiar to the reader.

It is apparent that if the trippers can be of the aboveground type, that type of installation would be advantageous.

The most widely used tripper is a strip of material that is stretched across the road, path, or corridor, so that the weight of a passing vehicle or person can be used to obtain the desired result.

One form of tripper has two vertically-spaced-apart metallic strips therein, and the weight of the passing objects caused the metallic strips to touch and thus complete an electric circuit. Not only is this form of tripper expensive, but the metallic strips soon corrode and destroy the usefulness of the tripper.

Another form of tripper is a sealed pressure tube that contains a given volume of air. The weight of a passing object collapses a portion of the tube, thus causing an increased air pressure that activates associated equipment. This system is satisfactory but it was found however, that the available pressure tubes had a limited life.

Prior-art pressure tubes took the form of hoses that had round cross sections. These had several disadvantages.

'Firstly, when struck by the tire of a vehicle, the round hose tended to roll away. This continued movement put a strain on the attachment to the utilization device.

Secondly, when the prior-art pressure hose had been moved as far as it could go by a first wheel or a first set of aligned Wheels, the succeeding wheel or set of aligned wheels to hit the tube stretched the tube, so that when the succeeding wheel or set of aligned wheels had passed, the pressure hose snapped back toward its original position. This continued movement and snapping-back caused a great deal of abrasion, and severely shortened the life of the pressure hose.

Thirdly, if the walls of the prior-art pressure hose were made thin enough to collapse under the Weight of the vehicle, this collapsing produced a great deal of stress on the walls, and they soon failed. If, on the other hand, the walls of prior-art pressure hoses were made thick enough to withstand the constant collapsing, they would not collapse under the weight of motorcycles or sports cars; and thus would not provide the desired results.

In an attempt to overcome the latter shortcoming, priorart pressure hoses used walls that incorporated strengthening materials such as fabrics; but these did not correct the shortcoming.

At the present time, pressure hoses are good for about half a million cycles; but this is too short a life for heavily travelled roads.

Objects and Drawings It is therefore the principal object of my invention to provide an improved tripper.

It is another object of my invention to that is sensitive to small weights.

It is a further object of my invention to provide a tripper that has a long life.

The attainment of these objects and others will be realized from the following specification, taken in conjunction with the drawings, of which FIGURE 1 is a diagrammatic representation of how my pressure tube is used;

FIGURE 2 is a cross sectional View of my pressure tube under normal uncollapsed conditions; and

FIGURE 3 is a cross sectional view of my pressure tube under collapsed conditions.

provide a tripper Brief Description of the Invention Detailed Description of the Invention As may be seen from FIGURE 1, in obtaining trafiic information, my pressure tube 10 is placed across a roadway 12. As previously indicated, it may be used in other locations; but for ease of explanation, its use will be discussed in terms of a road and vehicles.

The distal end 16 of pressure tube 10' is sealed. This result may be accomplished by doubling back the end of the tube, by insertin a plug into it, or in any other suitable manner.

The proximal end of pressure tube a utilization device 18, which may be a counter, a switch that controls signal lights or an alarm, a mechanism that opens or closes doors, or any other piece of apparatus.

While various arrangements may be used, the one shown in FIGURE 1 provides information on trafiic moving in a given direction; and places the utilization device on the shoulder of the roadway, where it may be checked, repaired, studied, etc. without danger from passing vehicles.

In FIGURE 2, there is shown a cross sectional view of my pressure tube 10' in its normal uncollapsed state. Tube 10 is made of a resilient rubber-like or plastic-like material.

As may be seen, it has an air channel 19, and the bottom 20' of the pressure tube 10 is concave, so that the pressure tube normally sits on its longitudinal edges 22. As soon as a wheel 24 of a vehicle strikes pressure tube 10, the longitudinal edges 22 are pressed tightly against roadway 12, so that the pressure tube cannot skid, bounce, or be moved from its original position. Further movement of Wheel 24 flattens out the concave bottom 20 of my pressure tube, and further deters movement of my pressure tube.

It will be seen that the above road-holding action keeps the pressure tube at substantially the same location at all times; and thus overcomes some of the shortcomings of prior-art pressure hoses.

In FIGURE 3, a cross sectional view of the pressure tube 10 is shown in its collapsed state. As previously explained, the resiliency of the material has permitted the bottom portion 20 to be flattened so that it, longitudi- 10 is attached to nal edges 22, and longitudinal ribs 26- are all in intimate contact with roadway 12.

The weight of the wheel (not shown) has also collapsed the pressure tube so that air duct 19 has also been collapsed. Depending upon the weight of the vehicle, the side portions 28 of the air duct 19 may be still partially open, so that the pressure is equalized throughout the pressure tube.

It will be noted from FIGURE 3 that the thick side walls 30 of the pressure tube 10 support the weight of the vehicle, due to the substantially greater mass of the material that form side walls 30, the relatively thin upper wall 32 of air duct 19 collapsing easily without excess deformation. I also believe that the oblong shape of the air duct directs lines of stress downward and outward to the greater body of rubber, which is better able to absorb them. This means that my structure overcomes the walltlexing characteristic of prior-art pressure hoses; and obviates the failures due thereto. I

Once the wheel of the vehicle has passed over my pressure tube, the resiliency of the material causes it to spring back to its normal uncollapsed condition.

At the present time, a sample of my pressure tube has undergone over two million cycles; and shows no appreciable sign of deterioration. Estimates of experienced traflic analysts are that it should be able to withstand many more cycles before having to be replaced.

Advantages It will be obvious that my pressure tube has many adparture from the spirit and scope of the invention, and that the specification and drawing are to be considered as merely illustrative rather than limiting.

I claim: v

1. A pressure tube comprising a length of resilient material having a cross section that approximates a semioval, said tube having a bottom wall, side walls and a top wall defining a longitudinal passage substantially centrally therethrough, said passage being substantially oblong in cross section having a major axis of substantial length -which has a minimum length of approximately one-third the width of the tube, the longitudinal axis of the passage being parallel to the longitudinal axis of the tube and the short ends of the oblong being rounded, the outer surface of said side walls and top wall joining to form a smoothly convex surface extending from substantially the bottom of one side wall to substantially the bottom of the other side wall, the outer surface of said bottom wall being slightly concave transversely of the tube so that said tube normally rests on its longitudinal edges, said top wall being of such thickness and material that it is readily collapsed by the weight of an overriding object, of substantial weight.

2. The tube for a trafiic indicator as set forth in claim 1 wherein said tube has a plurality of transversely spaced longitudinal ribs on the outer surface of the bottom wall.

3. The tube for the traflic indicator as set forth in claim 2 wherein the vertices of the ribs'define a concave outline.

4. The tube for a traffic indicator as set forth in claim 2 wherein the ribs are of triangular cross section and have their apexes disposed downwardly.

References Cited in the file of this patent UNITED STATES PATENTS 1,915,167 Salsbury June 20, 1933 2,107,350 Stubbins Feb. 8, 1938 2,440,533 Antonson Apr. 27, 1948 2,750,232 Szantay et al. June 12, 1956 Beachan et a1. Jan. 26, 1960 

1. A PRESSURE TUBE COMPRISING A LENGTH OF RESILIENT MATERIAL HAVING A CROSS SECTION THAT APPROXIMATES A SEMIOVAL, SAID TUBE HAVING A BOTTOM WALL, SIDE WALLS AND A TOP WALL DEFINING A LONGITUDINAL PASSAGE SUBSTANTIALLY CENTRALLY THERETHROUGH, SAID PASSAGE BEING SUBSTANTIALLY OBLONG IN CROSS SECTION HAVING A MAJOR AXIS OF SUBSTANTIAL LENGTH WHICH HAS A MINIMUM LENGTH OF APPROXIMATELY ONE-THIRD THE WIDTH OF THE TUBE, THE LONGITUDINAL AXIS OF THE PASSAGE BEING PARALLEL TO THE LONGITUDINAL AXIS OF THE TUBE AND THE SHORT ENDS OF THE OBLONG BEING ROUNDED, THE OUTER SURFACE OF SAID SIDE WALLS AND TOP WALL JOINING TO FORM A SMOOTHLY CONVEX SURFACE EXTENDING FROM SUBSTANTIALLY THE BOTTOM OF ONE SIDE WALL TO SUBSTANTIALLY THE BOTTOM OF THE OTHER SIDE WALL, THE OUTER SURFACE OF SAID BOTTOM WALL BEING SLIGHTLY CONCAVE TRANSVERSELY OF THE TUBE SO THAT SAID TUBE NORMALLY RESTS ON ITS LONGITUDINAL EDGES, SAID TOP WALL BEING OF SUCH THICKNESS AND MATERIAL THAT IT IS READILY COLLAPSED BY THE WEIGHT OF AN OVERRIDING OBJECT, OF SUBSTANTIAL WEIGHT. 